1. Field of the Invention
The present invention relates to radio IC devices including a radio IC and a radiation electrode pattern, and in particular, to a radio IC device used in an RFID (Radio Frequency Identification) system.
2. Description of the Related Art
In recent years, RFID systems, in which a reader/writer that generates an induction field and an IC tag (hereinafter referred to as a radio IC device) that is attached to an article and stores predetermined information communicate with each other by a non-contact method using an electromagnetic field to transmit the predetermined information, have been developed as an article management system.
Radio IC devices used in such an RFID system include a radio IC chip that processes a predetermined radio signal and a radiation electrode pattern that performs transmission and reception of the radio signal, and a known radio IC device is described in, for example, International Patent Publication No. WO2007/083574.
The radio IC device in International Patent Publication No. WO2007/083574 includes a radio IC chip, a feeder circuit board, on which the radio IC chip is mounted, which is provided with a feeder circuit including a resonant circuit having a predetermined resonant frequency, and a radiation electrode pattern which is attached to the lower surface of the feeder circuit board, and which radiates a transmission signal supplied from the feeder circuit and receives and supplies a reception signal to the feeder circuit. The radio IC device is designed so that the resonant frequency of the resonant circuit of the feeder circuit board substantially corresponds to the frequency of the transmission/reception signals, and thus, has a very stable frequency characteristic.
In the radio IC device described in International Patent Publication No. WO2007/083574, the frequency of the radio signals transmitted from/received by the radiation electrode pattern is substantially determined in the feeder circuit of the feeder circuit board, and thus, is nearly independent of the size or shape of the radiation electrode pattern. In addition, in International Patent Publication No. WO2007/083574, a technique for providing the radio IC chip on a rigid feeder circuit board and coupling the feeder circuit and the radiation electrode pattern to each other through a magnetic field or an electric field is disclosed as a technique to facilitate providing the radio IC chip on the radiation electrode pattern.
However, when the feeder circuit board and the radiation electrode pattern are coupled to each other through a magnetic field or an electric field, when the positional accuracy of mounting the feeder circuit board on the radiation electrode pattern is reduced, a transmission efficiency for signal energy from the feeder circuit to the radiation electrode pattern or from the radiation electrode pattern to the feeder circuit, that is, an efficiency in transmitting signals from the radio IC chip to the radiation electrode pattern or from the radiation electrode pattern to the radio IC chip, is likely to be reduced.